Test method for determination of free glycerol in Biodiesel by HPLC

Because of Bio-diesel outstanding environmental protection and renewable characteristic, more and more nations are paying attention to it. The content of free glycerin in Biodiesel is one of important targets to evaluate Bio-diesel. In the study, by using high capacity C18 SPE column to remain the major component(long-chain fatty acid alkyl ester) in Bio-diesel in order to eliminate its interfering with determination of minor component ( free glycerin) in Bio-diesel, and at same time free glycerin was eluted by water and methanol. With this kind of sample pretreatment, free glycerol in biodiesel could be enriched and analyzed by HPLC easily, even when the content of free glycerol in biodiesel is as low as 10ppm. The analytical method not only could meet the demand of testing free glycerin in Bio-diesel by GB/T 20828-2007, but also be convenient and fast. It could be used to analyze free glycerin in various Bio-diesels. The average recoveries of two samples ranged from 95.7% to 105.7% while the relative standard deviation was 0.6%∼8.8 %(n=6). When the amount of biodiesel (1.5g) for determination is used, the LOD was 28ppm (S / N = 3).